A Coriolis flowmeter is a mass flowmeter utilizing the fact that when a flow conduit through which a fluid to be measured flows is supported at one or both ends thereof, and an oscillation in a direction perpendicular to the flowing direction of the flow conduit is applied to a portion of the flow conduit around the support point, the Coriolis force acting on the flow conduit (Hereinafter, the flow conduit to which oscillation is to be applied will be referred to as the flow tube) is proportional to the mass flow rate. The Coriolis flowmeter is well known, and flow tube configurations of the Coriolis flow tube are roughly classified into a straight tube type and a bent tube type.
In the straight tube type Coriolis flowmeter, when an oscillation is applied to the central portion of a straight tube supported at both ends in a direction perpendicular to the straight tube axis, there is obtained, between the support portions and the central portion of the straight tube, a difference in straight tube displacement due to a Coriolis force, that is, a phase difference signal, and a mass flow rate is detected based on this phase difference signal. The straight tube type Coriolis flowmeter has a simple, compact, and firm structure. However, it also has a problem in that it cannot attain high detection sensitivity.
In contrast, the bent tube type Coriolis flowmeter is superior to the straight tube type Coriolis flowmeter in that it is possible to select a configuration for effectively extracting the Coriolis force; in fact, the bent tube type Coriolis flowmeter can detect mass flow rate with high sensitivity. Known examples of the bent tube type Coriolis flowmeter include one equipped with a single flow tube (see, for example, JP 04-55250 B), one equipped with two parallel flow tubes (see, for example, JP 2939242 B), and one equipped with a single looped flow tube (see, for example, JP 05-69453 B).